Thermally operated electric switch



Aug. 2l, 1951 l. E. MCCABE THEIRMALLY OPERATED ELECTRIC SWITCH Patented Aug. 21, 1951 vUNITED STATES PATENT OFFICE TBERMALLY OPERATED ELECTRIC SWITCH Ira E. McCabe, Chicago, Ill.

Application February 5, 1945, Serial No. 576,169

The present invention relates to enclosed mercury switches and more particularly to an enclosed switch structure which when connected to a source of electrical energy operates to intermittently make and break the circuit passing therethrough.

Mercury switches of the general type above described have certain inherent advantages which make them particularly useful under varying conditions to which the same may be subjected. Such switches are characterized as being adapted for use over long periods of time, immunity from oxidization or pitting of the contacts, and the complete sealing of the operating switch parts to effectively exclude dust and dirt and to prevent corrosion, all of which would otherwise affect the operation and life of the switch elements. In addition, such switches have the further characteristic of being highly suitable for use in high humidity and explosive charged atmospheres where the ordinary type of open solid metal to metal contacts would provide faulty or hazardous operation.

Accordingly, it is an object of the present i11- vention to provide a novel type of mercury switch having switch operating mechanism sealed within the container therefor and which mechanism is adapted to be connected to an electrical circuit for controlling said circuit intermittently. More particularly, the invention comprehends a switch operating mechanism including a movable part controllable through the medium of spring tension in one direction of movement thereof and controllable in the other direction of movement thereof by an expansible element whereby the movable part is adapted through the medium of a body of mercury to make and break a circuit ln which the switch mechanism is incorporated.

In one form of the invention the switch structure is provided with a iixed electrode in electrical connection with a capillary tube having one end immersed within a pool of mercury to provide a meniscus of mercury above the surface of the pool and with which is associated a spring actuated contact controlled by an expansible member for making and breaking an electrical circuit.

Another object of the present invention is to provide a. switch structure of the mercury type in which mercury is employed as a conductor for use in connection with 'enclosed switch operating mechanism to avoid the necessity for a mechanical snap action structure to make and break the circuit contacts whereby the switch 2 Claims. (Cl. Zoll- 113) 2 structure is greatly simplified and is more easily manufactured.

In the preferred forms ci the invention, the switch possesses the advantages of the switch assembly shown in applicants Patent No. 2,325,785 which embodies a capillary tube immersed in a defined well of mercury to present a meniscus of mercury above the level of the pool and with which is associated a tensioned contact controlled vby an expansible element whereby said contact is movable into and out of engagement with said meniscus of mercury.

Another object of the present invention is to provide a mercury switch of the type hereinabove set forth wherein the capillary tube is associated with a xed electrode therefor and the movable contact has an electrical connection with another electrode for the switch which includes the expansible element for control of the contact member.

The present invention in one of its forms comprehends a switch structure in which the movable contactis provided on a iexible element normally under tension to dispose the contact in engagement with the meniscus of mercury but which flexible element and contact is controlled by an expansible element adapted to elongate upon completion of the electrical circuit through the switch to permit the flexible element to disengage the contact from the meniscus of mercury whereby the switch can be operated to intermittently make and break the vcircuit passing therethrough.

Other objects, features, and capabilities and advantages are comprehended by the invention, as will later appear and as are inherently possessed thereby.

Referring to the drawings:

Figure 1 is a view in section of a switch structure made in accordance with the present invention;

Figure 2 is a view in section of a modified form of switch structure also made in accordance with the present invention;

Figure 3 is a view in cross section of still another modification of the invention; and

Figure 4 is a view in cross section of still a further modied form of construction for a switch made in accordance with the present invention.

Referring now more in detail to the drawings, an embodiment selected to illustrate the present invention is shown in Figure 1 as comprising an hermetically sealed container 2 of glass or other non-conducting material which is provided in the McCabe Patent No. 2,325,785. The capillary tube 8 is supported by a iixed electrode Il extending through the inner chamber l2 ofl the container 2 and through the sealed end I4 for the said container.

A second electrode I6 likewise extends through( 'the sealed end I4 of the container and into the chamber I2 thereof. Independently mounted as at I8 within a bead of glass or non-conducting material is a support 28 for a U-shaped spring element 22, the latter being connected at one of its ends to the support 28 and having its other end connected to a contact supporting element 24 formed with an inwardly extending contact part 26 in opposed relation to the opening I 0 in the capillary tube 8. The spring element 22 is adapted to normally urge the contact 26 out of engagement with the meniscus of mercury in the capillary tube 8 .and into the position as shown in dotted lines at 28. For control of the movement of the contact 26, an expansible and contractible element 30 is provided, the same being connected at one of its ends, as at 32, to the second electrode I6 and at its other end, as at 34, to the free end of the spring element 22 which is connected to the contact support 24.

As will be clearly appreciated, when no cul'- rent is passing through the electrodes il and I6, the contact 26 is under control of the expansible member 30 which in its cold condition is contracted to place the spring 22 under tension and to maintain contact 26 in engagement with the meniscus of mercury in the capillary tube 8. Upon the completion of a circuit through the switch. however, the element 38 is affected by the passage of current therethrough, thus raising its temperature and causing the same to elongate to relieve the tension inspring-member 22 and to cause the contact and its support to assume the dotted line position 28 for breaking the circuit through the switch. Breaking of the circuit causes the control element 3|! to cool and contract. thus placing the spring element 22 again under tension and to move the contact 26 into engagement with the meniscus of mercury in the capillary tube 8.

If desired, the invention may take the form as shown in Figure 2 of the drawings wherein the container 2 is provided with a well 4 adapted to serve as a reservoir for a pool of mercury 6. In this modication a capillary tube 36 is provided, the same being formed with an opening 38 to provide a meniscus of mercury disposed above the surface of the pool. The capillary tube 36 is supported by the electrode 40 extending through the chamber 42 of the container and outwardly through the sealed end 44 thereof.

This formof the invention likewise incorporates a second electrode 46, extending through the sealed end 44 oi.' the container and through the chamber 42 and terminating in spaced relation to the well 4. A movable contact 48 which is adapted to be moved into and out of engagement with the meniscus of mercury of the capillary tube 36 is carried by an element 58. Mounted as at 56 is an electrical conductor for support of element 60 through the medium of a coil spring 62. The conductor 54 is in electrical communication with the second electrode 46 through the medium of an expanslble and contractible element 58 having one of its ends secured as at 66 to the conductor 62 electrically connected to the conductor 54 and having its other end connected as at 64 to the second electrode 46. The expansible and contractible element member 58 is interconnected with the contact support 50 by means of the wire element 66.

It will be clearly apparentirom the above description that when no current passes through the switch structure, the expanslble element 58 is contracted and through the wire element 66 holds the contact 48 in engagement with the meniscus of mercury of the capillary tube 36. However, upon theV completion of a circuit through the switch, the temperature of the element 58 is raised, causing the same to elongate and to bow so as to allow the contact support 50, under the action of coil spring 52, to move away from the capillary tube 36 and to cause disengagement of the contact 48 with the meniscus of mercury therein. Upon a breaking of the circuit, the e1ement58 contracts, thus causing movement of the contact support 56 toward the electrode 40 whereby contact 48 again engages the mercury in the capillary tube 36. Intermittent making and breaking of the circuit is thereby accomplished, all in accordance with the preceding description.

In Figure 3 another embodiment of the invention is disclosed, the same comprising a sealed container 2 formed with the well 4 for receiving and holding a pool of mercury 6 and in which is immersed the end of a capillary tube 68 having an opening I0 providing a meniscus of mercury above the level of the pool, all in accordance with the previously described embodiments. In this structure the capillary tube 68 is supported by electrode 'I2 extending through the chamber 14 of the container 2 and outwardly through the sealed end 16 thereof. The switch is likewise formed with a second electrode 18 extending through the sealed end 'I6 of the container and being mounted as at in the chamber I4 thereof. Independently mounted as at 82 is a flexible contact supporting element 84 having a contact 86 at its other end adapted to be moved into and out oi engagement with the meniscus of mercury in the capillary tube 68.

Control of the movement of the ilexible supporting element 84 and its associated contact 86 is provided through the medium of an expansible and contractible lelement 88 connected to the electrode 18 asA at 90 and to the contact assembly at at 92. The length oi member 88 when contracted is such as to normally hold the contact supporting element 84 in a bowed condition with contact 86 in engagement with the meniscus of mercury in tube 68. Upon the completion of a circuit through the switch, the temperature of afmember 88 is raised, thus causing 2 formed with the well 4 serving as a reservoir for a body of mercury 6 and also embodies a switch structure generally referred to as 94 conforming in all essential respects with the switch mechanism of Figure 3 of the drawings.

In addition to the switch mechanism 94, there is provided an electrode 96 having a contact 98 at the lower end thereof which is adapted to be moved into and out of engagement with the mercury in the capillary tube |00 through an additional opening |02 provided therein. The contact 98 through the medium of element |04, which is an electrical nonconductor, is interconnected with the contact 06 of the switch mechanism 94.

The structure as shown in Figure 4 of the drawings provides for the control of substantially larger currents than possible with the previous structures hereinbefore disclosed without sacrificing the sensitivity of operation desired of the switch. Furthermore, a control circuit initiating and terminating the flow of current to a controlled device may be of low current capacity, a fact attributable to the sensitive low current capacity of the types of devices used in the controlling circuit. In this form of the invention, the second movable contact 98 is adapted to provide a two-circuit arrangement of the switch so that, as the intermittent make and break of the controlling mechanism is brought about, its action is accompanied by an intermittent opening and closing of the heavier capacity movable contact in the controlled device circuit. In effect, therefore, the present switch provides a unitary control assembly for controlling a circuit which eliminates a separate relay for handling larger loads as would be the case in the event that the structures of Figures l, 2 and 3 were used for controlling circuits of capacities larger than that which the switch itself was capable of handling.

In all forms of the invention, the capillary tube provided as a part of the switch operating mechanism provides a small body of mercury with a small surface area presented for contact with the movable contact which makes it possible to make use of a contact point readily wetted by mercury to provide a snap action operation with a, minimum of contact movement being necessary to effect the operation of the switch. By use of a contact point including a portion which wets readily with mercury, it is possible to cause the mercury to adhere to and to stretch out as the contact departs therefrom until a complete break has been effected, thus providing a quick break in the circuit which, when made, creates aftgap sufficient to prevent any fluttering therea er.

Furthermore, the expansible and flexible elements of the switch structure may be made of such material that their temperature coeflicient of expansion is alike whereby the effect of ambient temperature changes upon the operating characteristics of the switch may be nullied.

In the manufacture of glass enclosed switch mechanisms of the type herein disclosed, the heating of the glass preparatory to the application of the press which seals the mechanism for support therein, and the annealing processes which follow, so raises the temperature that the mechanism or parts to be sealed in can be caused to change their operative relationships from those which it is desired and for which the same were originally designed. As a consequence, adjustment is desired after such sealing operations to provide for the proper and intended operation of determined.

the switch. The present forms of the invention lend themselves readily to such adjustments. As shown in Figure 1 of the drawings, the well end of the tube may -be initially formed as a round tubular projection such as shown in dotted lines at |06. With the end open as disclosed, suitable tools may be inserted to position and adjust the parts as the necessity for the same is needed and After such adjustments have been made for the performance desired, the open end may be molded closed to provide the well 4 for the mercury. The switch then may be processed to completion with the exhausting and filling tube sealed in the pressed end,.tipped off, to provide the hermetically sealed mercury switch desired.

In the type of switch hereinabove described, the capillary tube which is used provides a fixed contact surfacev and although arcing and consequently vaporization may occur, a well or reservoir of mercury constantly provides the contact meniscus of mercury. Condensation of the mercury upon the walls of the glass tubes eventually forms in large globules which roll back into the well. Thus this construction is susceptible to being made to handle larger currents than other forms in which vaporization through operation varies the volume and surface of the mercury presenting the contact surface.

In addition, it will also be apparent that the timing desired may in part be had by varying the distance between the fulcrum or pivotal point of the flexible contact wire and the point of attachment thereto of the expansible element.

While I have herein described and upon the drawings shown an illustrative embodiment of the invention, it is to be understood that the invention is not limited thereto but may comprehend other constructions, arrangements of parts, details and features without departing from the spirit of the invention.

What is claimed is:

1. An electric switch comprising a sealed container, a pool of mercury within said container, movable and stationary contact members within said container, a capillary tube having electrical connection with said stationary contact member and being supported with one end thereof immersed within the pool of mercury, said capillary tube presenting a contacting surface of mercury above the pool for contact by said movable contact member whereby to close an electric circuit, said movable contact member being provided with a portion readily wetted by mercury to effect a positive electrical break with the contacting surface of mercury upon separation of the movable contact member therefrom, an expansible and contractible wire element within the container and included in the electric circuit for controlling movement of the movable contact member with respect to said contacting surface of mercury, an independently mounted contact member having a support adapted to be flexed and having a portion readily wetted by mercury, and means linking said independent contact member with the movable contact member whereby said independent contact member is also caused to move into and out of engagement with the contacting surface of mercury provided by said capillary tube.

2. An electric switch comprising a sealed container, a pool of mercury within said container, a plurality of contact members within said container comprising a first contact member having a portion readily wetted by mercury and a second contact member, a capillary tube associated with the second contact member and having an end thereof immersed within the pool of mercury, said capillary tube presenting a contacting surface of mercury above the pool for contact by said rst contact member, the wetted portion ot said i-lrst contact member effecting a positive electrical break with said contacting surface of mercury upon separation therefrom. spring means for yieldingly biasing one of said contact members toward one of its contact positions, an expansible and contractble wire element within the container adapted, when contracted, to overcome the force of said spring means and position the said spring biased contact member in a second contact position, said wire element being included in the electric switch circuit for controlling the contact position of the spring actuated contact member, a third contact member having a portion readily wetted by mercury, a contacting surface of mercury therefor presented by said capillary tube, said third contact member being adapted to en- 8 gage said contacting surface upon movement of the spring actuated contact member to one of its contact positions.

IRA E. MCCABE.

d REFERENCES CITED The following references are of record in the Number Name Date 1,289,637 Bruce Dec. 31, 1918 1,774,109 Phelan Aug. 26, 1930 1,826,572 Phelan et al Oct. 6, 1931 1,882,614 Hunciker Oct. 11, 1932 1,897,454 Walder et al Feb. 14, 1933 2,042,865 Ruttenberg June 2, 1936 2,121,235 Hunciker June 21, 1938 2,299,767 Schmidinger Oct. 27, 1942 2,325,785 McCabe Aug. 3, 1943 

